As the data transmission bandwidth increases with the development of communication technology, users' demand for high-quality communication services using multi-channel voice and audio increases. A coding scheme capable of effectively compressing and decompressing stereo voice and audio signals is necessary to provide high-quality voice/audio communication services.
Accordingly, extensive research is being conducted on a codec for coding narrowband (NB, 300˜3,400 Hz) signals, wideband (WB, 50˜7,000 Hz) signals, and super-wideband (SWB, 50˜14,000 Hz) signals. An ITU-T G.729.1 codec is a typical example of a wideband extension codec based on a G.729 narrowband codec. The ITU-T G.729.1 wideband extension codec provides a bitstream-level compatibility with the G.729 narrowband codec at 8 kbit/s, and provides narrowband signals of improved quality at 12 kbit/s. Also, the ITU-T G.729.1 wideband extension codec can encode wideband signals with a bit-rate extensibility of 2 kbit/s from 14 kbit/s to 32 kbit/s, and can improves the quality of an output signal with an increase in the bit rate.
Recently, an extension codec capable of providing super-wideband signals based on G.729.1 is being developed. This extension codec can encode and decode narrowband, wideband and super-wideband signals.
The extension codec may use sinusoidal pulse coding to improve the quality of a synthesized signal. The sinusoidal pulse coding may be performed through a plurality of layers. If the number of pulses or bits allocated for sinusoidal pulse coding by a lower layer varies on a frame-by-frame basis, it is necessary to provide a scheme for improving the quality of a synthesized signal in sinusoidal pulse coding by an upper layer.